Development of (Cr,Al)ON coatings using middle frequency magnetron sputtering and investigations on tribological behavior against polymers

Plastic processing is an enormous and expanding commercial sector. Injection molding and extrusion are common techniques for worldwide efficient mass production of plastic components with high shape accuracy and high surface quality for a broad variety of applications. Adhesive and abrasive wear as well as corrosion taking place during the production of plastic products and high deforming forces lead to the necessity of developing new material concepts. Ternary nitride and oxide hard coatings deposited by PVD (physical vapor deposition) find widespread application as hard protective coatings against wear and corrosion due to their outstanding tribological, mechanical and chemical properties. Besides ternary nitrides and oxides, quaternary chromium based oxy-nitride coating systems as (Cr1 − xAlx)ON are promising candidates for tribological applications revealing high potential for decreasing adhesion and deforming forces between PVD coated tool and plastics melt during the production, e.g. of optical components or microstructered parts. The present work deals with the development of chromium based oxy-nitride hard coatings (Cr1 − xAlx)ON on tool steel AISI 420 (X42Cr13, 1.2083) using middle frequency (mf) pulsed magnetron sputtering (MS) PVD technology. The aluminum content of the (Cr1 − xAlx)ON coatings was varied in the range of 10.3 at.-% and 68.0 at.-%. By means of optical emission spectroscopy (OES) the deposition process was monitored regarding Cr/Cr+ and Al/Al+ ratios and the working points were varied via oxygen gas flow. Morphology, mechanical properties, phase and chemical composition were analyzed. Adhesion behavior between (Cr1 − xAlx)ON coatings towards plastics by high temperature contact angle measurements revealed a significant impact of the coatings' chemical composition determined by depth resolved electron probe micro analysis (EPMA). Tribological model tests in a pin-on-disk-tribometer verified a positive influence of (Cr1 − xAlx)ON coatings on the adhesion behavior towards polymers which is directly linked to lowering of deforming forces. This makes oxy-nitride (Cr1 − xAlx)ON hard coatings a promising candidate for the production of optical components or microstructured parts by injection molding or extrusion.